How do I include a locally defined function when using PowerShell's Invoke-Command for remoting?

I feel like I'm missing something that should be obvious, but I just can't figure out how to do this.

I have a ps1 script that has a function defined in it. It calls the function and then tries using it remotely:

function foo
{
    Param([string]$x)

    Write-Output $x
}

foo "Hi!"

Invoke-Command -ScriptBlock { foo "Bye!" } -ComputerName someserver.example.com -Credential [email protected]

This short example script prints "Hi!" and then crashes saying "The term 'foo' is not recognized as the name of a cmdlet, function, script file, or operable program."

I understand that the function is not defined on the remote server because it is not in the ScriptBlock. I could redefine it there, but I'd rather not. I'd like to define the function once and use it either locally or remotely. Is there a good way to do this?

Solution 1:

You need to pass the function itself (not a call to the function in the ScriptBlock).

I had the same need just last week and found this SO discussion

So your code will become:

Invoke-Command -ScriptBlock ${function:foo} -argumentlist "Bye!" -ComputerName someserver.example.com -Credential [email protected]

Note that by using this method, you can only pass parameters into your function positionally; you can't make use of named parameters as you could when running the function locally.

Solution 2:

You can pass the definition of the function as a parameter, and then redefine the function on the remote server by creating a scriptblock and then dot-sourcing it:

$fooDef = "function foo { ${function:foo} }"

Invoke-Command -ArgumentList $fooDef -ComputerName someserver.example.com -ScriptBlock {
    Param( $fooDef )

    . ([ScriptBlock]::Create($fooDef))

    Write-Host "You can call the function as often as you like:"
    foo "Bye"
    foo "Adieu!"
}

This eliminates the need to have a duplicate copy of your function. You can also pass more than one function this way, if you're so inclined:

$allFunctionDefs = "function foo { ${function:foo} }; function bar { ${function:bar} }"